The present invention is related to a document pressing structure in a scanning device, and more particularly to a document pressing structure in a flatbed scanner.
To use a flatbed scanner, a document is placed on a glass platform of the scanner, and then pressed by a cover for positioning, and thereafter, the scanner is actuated to perform scanning operations.
It is generally required that the entire scanned face of the document press against the glass platform as close as possible owing to the requirement of constant depth of field for the sensing device, such as a charge coupled device (CCD) or a contact image sensor used, in the scanner (CIS) to pick up the image of the scanned face. Especially for a CIS, the closeness between the document and the platform is strictly required.
As known, the closeness between a document and a platform on which the document is placed cannot be assured if the document is simply placed on the platform without exerting thereon any pressing force. For example, the creases of the document are likely to cause the depth of field to be beyond an acceptable range. Therefore, a pressing force is generally exerted on the document in order to press the entire scanned face of the document against the platform close.
Please refer to FIG. 1 which is an exploded structural diagram schematically showing the pressing of the document with a weighty material in a conventional flatbed scanner. The scanner shown in FIG. 1 includes a cover frame 11, a metal plate 12, polyurethane foam 13, a document pressing plate 14, a scanner housing 15, and a glass platform 16. The metal plate 12, polyurethane foam 13, and document pressing plate 14 are combined together into the cover frame 11 to form a cover 10. When a document is to be scanned, the document is placed on the platform 16 and the cover 10 is pivoted onto the documents so as to press the document between the pressing plate 14 and the glass platform 16. The weight of the metal plate 12 provides a downward pressing force for the document to press the document close to the platform 16. The polyurethane foam 13 serves as a cushion to protect the glass platform 16 and further enhance the close contact between the scanned face of the document and the platform 16.
Although such a cover provides good pressing effect, the presence of the metal plate not only results in high cost of the scanner, but also renders inconvenient the lifting operation of a user owing to its high weight.
Therefore, an object of the present invention is to provide a document pressing structure for a flatbed scanner which causes a document to be scanned to be exposed close to a scanning platform of the scanner without adding weight to the cover of the scanner.
The present invention is related to a document pressing structure in a flatbed scanner. The flatbed scanner includes a housing and a cover over the housing. A transparent platform is mounted on a top surface of the housing for supporting a document to be scanned, and the cover has a first side thereof pivotally connected to a first side of the top surface of the housing for shielding the document from external light when the cover is pivoted to a closed position. The document pressing structure according to the present invention includes a First coupling element mounted on a second side of the cover, and a second coupling element mounted on a second side of the top surface, wherein the first and the second coupling elements are engaged with each other when the cover is pivoted to the closed position so as to allow the cover to press a scanned face of the document close to the transparent platform.
Preferably, the transparent platform is a glass platform. The second side of the cover is opposite to the first side of the cover, and the second side of the top surface is opposite to the first side of the top surface.
In a preferred embodiment, the first coupling element is a downwardly depending flexible piece with a horizontal projection, the second coupling element is a recess in a complementary projecting member, and when the flexible piece slides into the recess, upper bevel of the projection engages a lower bevel forming an upper surface of the recess when the cover is pivoted to the closed position.
In another preferred embodiment, the first coupling element is a magnetic piece inlayed in the cover, the second coupling element is another magnetic piece inlayed in the housing, and the two magnetic pieces are engaged with each other by magnetic force when the cover is pivoted to the closed position.